Methods of forming metal oxide nanostructures, and nanostructures thereof

ABSTRACT

A method of forming a metal oxide nanostructure comprises disposing a chelated oligomeric metal oxide precursor on a solvent-soluble template to form a first structure comprising a deformable chelated oligomeric metal oxide precursor layer; setting the deformable chelated oligomeric metal oxide precursor layer to form a second structure comprising a set metal oxide precursor layer; dissolving the solvent-soluble template with a solvent to form a third structure comprising the set metal oxide precursor layer; and thermally treating the third structure to form the metal oxide nanostructure.

BACKGROUND

The present disclosure is generally related to methods of forming metaloxide nanostructures and nanostructures thereof, in particular, titaniananostructures.

Titania is a well-know material with a broad range of applicationsincluding photonic crystals, photocatalysts, and photovoltaic cells.While several methods are known for nanostructuring titania, includingthermal imprinting, many challenges remain mainly due to the propertiesof commonly-used sol-gel type titania precursors. The sol-gel typetitania precursors are formed at low pH (approximately 1), are generallyhighly reactive and moisture sensitive, and form gels. They are oftendiluted in organic solvents during the sol-gel reaction to mitigategelation, which causes large volume shrinkages during thenanostructuring process. Further, they are usually highly viscous andrequire high pressure for the nanostructuring process. Prior workdirected toward thermal imprinting titania nanostructures used sol-geltype precursors [C. Goh, K. M. Coakley, M. D. McGehee, Nano Lett. 5,1545 (2005), P. Yang, T. Deng, D. Zhao, P. Feng, D. Pine, B. F. Chmelka,G. M. Whitesides, G. D. Stucky, Science, 282, 2244, (1998)] or a mixtureof titania colloidal particles and polymers [M. Wang, H.-G. Braun, andE. Meyer, Chem. Mater. 14, 4812 (2002)].

BRIEF SUMMARY

Preferred aspects of the present invention are methods that employ ametal oxide material that has optimal properties for the process, suchas low viscosity, controlled reactivity, UV-curability, and structuralstability during calcination.

In one aspect, a method of forming a metal oxide nanostructure comprisesdisposing a chelated oligomeric metal oxide precursor on asolvent-soluble template to form a first structure comprising adeformable chelated oligomeric metal oxide precursor layer; setting thedeformable chelated oligomeric metal oxide precursor layer to form asecond structure comprising a set metal oxide precursor layer;dissolving the solvent-soluble template with a solvent to form a thirdstructure comprising the set metal oxide precursor layer; and thermallytreating the third structure to form the metal oxide nanostructure.

In another aspect, a method of forming a metal oxide nanostructurecomprises disposing a chelated oligomeric metal oxide precursor on asolvent-soluble template to form a first structure comprising a chelatedoligomeric metal oxide precursor layer having an exposed surface;bonding a substrate to an exposed surface of the chelated oligomericmetal oxide precursor layer to form a second structure comprising achelated oligomeric metal oxide precursor layer; setting the chelatedoligomeric metal oxide precursor layer of the second structure to form athird structure comprising a set metal oxide precursor layer; dissolvingthe solvent-soluble template with a solvent to form a fourth structurecomprising the set metal oxide precursor layer; and thermally treatingthe fourth structure to form a fifth structure comprising a metal oxidenanostructure bonded to the substrate.

In another aspect, a method of forming a metal oxide nanostructurecomprises disposing a chelated oligomeric metal oxide precursor on asubstrate to form a first structure comprising a deformable chelatedoligomeric metal oxide precursor layer; contacting a solvent-solubletemplate to the deformable chelated oligomeric metal oxide precursorlayer to form a second structure comprising a shaped chelated oligomericmetal oxide precursor layer; setting the shaped chelated oligomericmetal oxide precursor layer of the second structure to form a thirdstructure comprising a set metal oxide precursor layer; dissolving thesolvent-soluble template with a solvent to form a fourth structurecomprising the set metal oxide precursor layer; and thermally treatingthe fourth structure to form the metal oxide nanostructure.

Also disclosed are metal oxide nanostructures derived from a chelatedoligomeric metal oxide precursor.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

FIG. 1 is a schematic of the typical process flow of forming a metaloxide nanostructure by transfer molding.

FIG. 2 is a schematic of a transfer molding process to form a metaloxide nanostructure wherein a substrate is laminated to a deformablemetal oxide precursor layer prior to setting the metal oxide precursorlayer.

FIG. 3 is a schematic of the typical process flow of forming a metaloxide nanostructure by imprinting.

FIG. 4 is a set of scanning electron micrographs (SEM) images of ananostructured titania at different magnification. Samples were baked at450° C. for 2 hours.

FIG. 5 is a set of atomic force microscopy (AFM) (height contrast)images of a nanostructured titania. Samples were baked at 450° C. for 2hours.

FIG. 6 is a graph of the grazing angle X-ray diffraction of the titaniananostructure film.

FIG. 7 is a high-resolution transmission electron microscopy (HRTEM)image of the titania nanostructure film.

DETAILED DESCRIPTION

Disclosed methods of forming metal oxide nanostructures employnon-sol-gel type chelated oligomeric metal oxide precursors. Thechelated oligomeric metal oxide precursors can be easily thermallydeformable and have high solid content. Further, the solid content canbe controlled by the addition of solvent if desired. In particular thechelated oligomeric metal oxide is a titania precursor.

The following Scheme (I) illustrates a non-limiting example of thepreparation of a chelated oligomeric metal oxide precursor of generalformula (3) used in forming the metal oxide nanostructures. Chelatedoligomeric metal oxide precursor (3) is derived from a polymetalate ofgeneral formula (1) and a chelating agent of general formula (2). Thereaction does not require the presence of water or acid.

M in formulas (1) and (3) can be a metal selected from the groupconsisting of transition metals (Group 3 to Group 12 elements of theperiodic table) including lanthanides, zinc, aluminum, gallium, indium,thallium, germanium, tin, lead, antimony, bismuth, and combinationsthereof. In particular, M may be titanium. Each R in the polymetalate(1) can independently represent a group having 1 to 20 carbons. Morespecifically, R is an alkyl radical or branched alkyl radical selectedfrom the group consisting of methyl, ethyl, propyl, iso-propyl, n-butyl,iso-butyl, tert-butyl, pentyl, iso-pentyl, hexyl, heptyl, n-octyl, andcombinations thereof. Subscript x can be an integer equal to the metalvalence minus 2. Subscript n is an integer greater than or equal to 2;more specifically, n is an integer from 2 to about 1000. Even morespecifically, n is an integer from 2 to about 100; and still morespecifically, n is an integer from 2 to about 10. Subscript m is aninteger from zero to n−1.

The chelating agent (2) is an enolizable material; for example,beta-diketone, beta-keto acid, beta-keto ester, beta-keto amide, malonicdiester, malonic diamide, or combination thereof. R′ and R″ in formula(2) can independently contain 1 to 20 carbons representing an alkylradical, branched alkyl radical, aryl radical, or substituted arylradical. R′ and R″ can further independently represent an oxygen ornitrogen bearing group having 1 to 20 carbons, including substituted andunsubstituted members of the group consisting of alkoxy groups, aryloxygroups, primary alkylamino groups, secondary alkylamino groups, andtertiary alkylamino groups wherein the oxygen or nitrogen is bound toone or more of the carbonyl groups of formula (2). Exemplary chelatingagents include 1-phenyl-1,3-butanedione, 2,4-pentanedione(acetylacetone), 1,1,1-trifluoro-2,4-pentanedione, 2,4-hexanedione,5,7-nonanedione, benzoylacetone, dibenzoylmethane, 2′-napthaloylacetone, 9′-anthryloyl methane, diisobutyrylmethane,2,2-dimethylheptane-3,5-dione; 2,2,6-trimethylheptane-3,5-dione,2,2,6,6-tetramethyl-3,5-heptanedione, dipivaloylmethane, ethylacetoacetate, and tetramethylheptanedione. The chelating agent can alsobe a salen, alpha diketone bis oxime, or 7-hydroxyquinolate. The term“salen” is a contraction used to refer to those ligands typically formedthrough a salicylic aldehyde derivative with one molecule of a diaminederivative. While salen ligands are formed from ethylenediaminederivatives, propyl and butyl diamines can also be used to giveanalogous “salpn” and “salbn” derivatives.

The chelating agent is present in an amount of 10 mole percent to 100mole percent relative to metal ion; more particularly, 50 mole percentto 100 mole percent relative to metal ion; and even more particularly,75 to 100 mole percent.

In a specific embodiment, represented in Scheme (II), polytitanate ofgeneral formula (4) is treated with chelating agent (5) to formoligomeric chelated titanium oxide precursor of general formula (6).

R, R′, R″ and n have the same meaning as defined above for formulas (1)and (2). Subscript m can be an integer from zero to n−1. In a specificembodiment, R is n-butyl and n is an integer from 2 to about 10, m iszero, R′ is phenyl, and R″ is methyl.

FIG. 1 is a schematic of the process flow of forming a metal oxidenanostructure 50 by transfer molding. The transfer molding methodcomprises disposing the above-described chelated oligomeric metal oxideprecursor on a solvent-soluble template 22 to form a first structure 20comprising a deformable chelated oligomeric metal oxide precursor layer24 [C. D. Schaper, A. Miahnahri, J. Vac. Sci. Technol. B 22, 3323(2004), C. D. Schaper, Langmuir 20, 227 (2004), C. D. Schaper, NanoLett. 3, 1305 (2003)]; setting the deformable chelated oligomeric metaloxide precursor layer 24 of first structure 20 to form a secondstructure 30 comprising a set metal oxide precursor layer 34; dissolvingthe solvent-soluble template 22 with a solvent to form a third structure40 comprising the set metal oxide precursor layer 34; and thermallytreating the third structure 40 to form fourth structure 50 comprisingmetal oxide nanostructure 54.

Disposing the chelated oligomeric metal oxide precursor on asolvent-soluble template 22 can be accomplished by spray coating, dipcoating, meniscus coating, spin coating, or ink jet printing a liquidmixture comprising the chelated oligomeric metal oxide precursor in asuitable organic solvent, and removing the solvent. The shape of thetemplate determines the deposition technique and optimal conditionstherefor. Each would be readily apparent to the skilled artisan.Exemplary but non-limiting solvents include propylene glycol propylether (PGPE), propylene glycol methyl ether, propylene glycol methylether acetate, tetrahydrofuran, ethylene glycol dimethyl ether, diglyme,n-butanol, acetone, ethanol, isopropanol, toluene, anisole, chloroformand the like. The solvent can optionally include water. In a specificembodiment, the solvent does not include water.

After the initial deposition of the chelated oligomeric metal oxideprecursor, the resulting structure 20 can optionally be treated toobtain a solvent-free or otherwise stable, uniform thin film. In onetreatment, structure 20 can be heated to temperatures of from about 50°C. to about 150° C. for from about 1 minute to several hours, moreparticularly less than one hour. Another optional treatment involvessubjecting structure 20 to air flow or vacuum to remove residualsolvent. The deformable chelated oligomeric metal oxide precursor layer24 can have any suitable thickness, typically from about 0.05micrometers to about 1000 micrometers, more particularly about 1micrometer to about 100 micrometers.

“Setting” refers to forming a free-standing three-dimensional polymericnetwork of the metal oxide precursor. For example, the network can havethe form of a crosslinked gel. The set metal oxide precursor furthercomprises a carbon-containing component. Setting can be accomplished byknown methods, including UV-irradiation, electron beam irradiation,ionizing radiation, heating, or a combination thereof. In particular,UV-irradiation is employed to set the deformable oligomeric metal oxideprecursor layer. The UV-sensitivity of the oligomeric metal oxideprecursor can be suitably controlled by the choice and/or amount ofchelating agent associated with the metal in the chelated oligomericmetal oxide precursor. Without being bound by theory, setting isattributed to dissociation of the chelating agent from the chelatedoligomeric metal-oxide precursor causing the oligomers to crosslink intoa three-dimensional polymeric network.

Thermally treating the set metal oxide precursor layer to form the metaloxide nanostructure can be performed at a temperature of about 250° C.to about 950° C. More particularly, the thermal treatment is performedat a temperature of greater than about 400° C., and even moreparticularly about 450° C. to about 650° C., for a period of timesufficient to convert the set metal oxide precursor to a metal oxide.The thermal treatment can be by calcining. Calcining oxidatively removesthe carbon-containing component of the set metal oxide precursor,leaving only the metal oxide nanostructure. The time of thermaltreatment can be for a period of about 30 minutes to about 24 hours.

The metal oxide nanostructure has a crystalline structure that can beporous or non-porous. The pores can have a dimension of from 0.005micrometers to 10 micrometers, more specifically, 0.01 micrometers to0.1 micrometer.

In one embodiment the deformable chelated oligomeric metal oxideprecursor layer 24 is bonded to a substrate prior to setting, as shownschematically in FIG. 2. This method comprises disposing theabove-described chelated oligomeric metal oxide precursor on asolvent-soluble template 22 to form a first structure 20 comprising anchelated oligomeric metal oxide precursor layer 24 having an exposedsurface 26; bonding a substrate 62 to the exposed surface 26 of thechelated oligomeric metal oxide precursor layer 24 to form a secondstructure 60 comprising chelated oligomeric metal oxide precursor layer64; setting the chelated oligomeric metal oxide precursor layer 64 ofsecond structure 60 to form a third structure 70 comprising a set metaloxide precursor layer 74 bonded to the substrate 62; dissolving thesolvent-soluble template 22 with a solvent to form a fourth structure 80comprising the set metal oxide precursor layer 74 bonded to thesubstrate 62; and thermally treating the fourth structure 80 to form afifth structure 90 comprising the metal oxide nanostructure 94 bonded tothe substrate 62.

The substrate 62 can comprise a semiconductor material. Exemplarysemiconductor materials include but are not limited to: silicon,germanium, silicon-germanium alloy, silicon carbide andsilicon-germanium carbide alloy semiconductor materials. In addition,semiconductor materials can also include compound (II-VI and III-V)semiconductor materials of which gallium arsenide, indium arsenide andindium phosphide are non-limiting examples. In particular, the substratecomprises silicon, SiGe, SiC, and Ge. Other substrates include glass orfused silica and conductive substrates comprising a conductive metal ora conductive metal oxide deposited on quartz or glass. Conductive metalsinclude transition metals such as titanium, manganese, iron, nickel,copper, zinc, molybdenum, palladium, silver, platinum, and gold; GroupII metals such as magnesium, and Group XIII and XIV metals such asaluminum, gallium, indium, and tin; and combinations of the foregoingmetals. Conductive metal oxides include for example oxides of transitionmetals such as copper, gold, silver, platinum, palladium; oxides ofgroup 13 metals including indium and gallium; oxides of group 14 metals,specifically germanium, tin, and lead; oxides of group 15 elements,specifically arsenic, antimony, and bismuth; and combinations thereof.Specific metal oxides include tin oxide (SnO₂), fluorinated tin oxide,indium tin oxide (ITO, InSnO₂), zinc oxide (ZnO), or combinationsthereof deposited on glass or quartz. In particular, the metal oxide istransparent.

Bonding the substrate 62 to the chelated oligomeric metal oxideprecursor layer 24 can be effected by lamination techniques that includethe application of suitable heat and/or pressure to form secondstructure 60. Bonding can optionally include an adhesive interfacialsurface. The adhesive interfacial surface interposed between thesubstrate 62 and the oligomeric metal oxide precursor layer 24 canoptionally comprise a polymeric or non-polymeric adhesive material.Bonding is generally undertaken using a pressure laminating method.Bonding methods that use adhesive material interposed between thesubstrate 62 and the chelated oligomeric metal oxide precursor layer 24can be used as an adjunct or an alternative to a pressure laminatingmethod. The bonding adhesive should be thermally stable to the finalprocessing conditions of the ceramic nanostructure.

The template can be soluble in organic solvent, water, or mixturesthereof. No restriction is placed on the template composition, providingthe desirable properties of the template are not adversely affected; forexample, the solubility of the template after setting the oligomericmetal oxide precursor layer. In particular, the template comprises awater-soluble polymer. The water-soluble polymer can be soluble atacidic pH (0 to less than 7), alkaline pH (7 to 14), or both. Exemplarywater-soluble polymers include, for example, poly(vinyl alcohol) resinscomprising hydrophilic hydroxyl groups [e.g., poly(vinyl alcohol) (PVA),acetyl-modified poly(vinyl alcohol), cation-modified poly(vinylalcohol), anion-modified poly(vinyl alcohol), silanol-modifiedpoly(vinyl alcohol), and poly(vinyl acetal)], cellulose resins [e.g.,methyl cellulose (MC), ethyl cellulose (EC), hydroxyethyl cellulose(HEC), carboxymethyl cellulose (CMC), hydroxypropyl cellulose (HPC),hydroxyethylmethyl cellulose, and hydroxypropylmethyl cellulose],chitins, chitosans, starches, gelatins, polyethers [e.g., polyethyleneoxide (PEO), polypropylene oxide (PPO), polyethylene glycol (PEG), andpolyvinyl ether (PVE)], and resins comprising carbamoyl groups [e.g.,polyacrylamide (PAA), polyvinylpyrrolidone (PVP), and polyacrylichydrazide].

In a specific embodiment, the template consists essentially of polyvinylalcohol (PVA). The poly(vinylalcohol) can have a weight averagemolecular weight of from about 5,000 to about 100,000, and 80 to 99percent of the structural subunits are hydrolyzed; that is, thepoly(vinylalchohol) is derived from poly(vinyl acetate) by hydrolysis of80 to 99 percent of the acetate groups.

The template comprises a relief surface for forming a patterned layer ofchelated oligomeric metal oxide precursor. The relief surface can haveany topographic pattern suitable for the intended use of the metal oxidenanostructure. The relief surface of template 22 in FIGS. 1 and 2 isexemplary and not meant to be limiting.

When desirable, the template can comprise water-insoluble polymers andcopolymers for dissolution in an organic solvent; for example, thetemplate can comprise polystyrenes, polyacrylates, polymethacrylates,poly(vinyl esters), poly(vinyl alkylidenes), poly(vinyl chloride),polyesters such as poly(butylene terephthalate) and poly(ethyleneterephthalate), and polycarbonates.

The templates can comprise a water-insoluble polymer capable ofundergoing chemical deprotection to form water-soluble polymers. In oneexample, the template composition can comprise an acid-labile,water-insoluble polyacrylate and a photoacid generator. Acid mediateddeprotection of polyacrylate ester groups to carboxylic acid groups canbe initiated by suitably irradiating the photoacid generator componentcontained in the template, resulting in the release of acid. Heating theirradiated exposed structure containing the released acid can theninduce ester deprotection, forming a water-soluble template. Thetemplate can also be soluble in dilute aqueous alkali solutions (e.g.,0.25N sodium hydroxide, potassium carbonate, sodium bicarbonate,ammonia, and the like). Acid release can be coincident with setting theoligomeric metal oxide precursor; that is, during irradiative and/orthermal treatment; alternatively, acid release can occur in a differentirradiative and/or thermal treatment step.

The template can also be used for imprinting the chelated oligomericmetal oxide precursor on a substrate, as shown schematically in FIG. 3.The imprint method comprises disposing the chelated oligomeric metaloxide precursor on a substrate 102 to form a first structure 100comprising a deformable chelated oligomeric metal oxide precursor layer104; contacting a solvent-soluble template 106 to the deformablechelated oligomeric metal oxide precursor layer 104 to form a secondstructure 110 comprising a shaped chelated oligomeric metal oxideprecursor layer 114; setting the shaped chelated oligomeric metal oxideprecursor layer 114 of second structure 110 to form a third structure120 comprising a set metal oxide precursor layer 124; dissolving thesolvent-soluble template 106 in a solvent to form a fourth structure 130comprising the set metal oxide precursor layer 124; and thermallytreating the fourth structure 130 to form a fifth structure 140comprising a metal oxide nanostructure 144 disposed on substrate 102. Inone embodiment, the solvent-soluble template is dissolved with anacidic, basic or neutral aqueous solution.

Also disclosed are metal oxide nanostructures derived from a chelatedoligomeric metal oxide precursor by any of the above described methods.In one embodiment, the metal oxide nanostructure comprises titania. Thetitania can have a rutile, brookite, or anatase crystalline structure.In particular, the titania crystalline structure is anatase. The metaloxide nanostructure can also be porous or nonporous after thermaltreatment at temperatures above about 400° C.

The following non-limiting example illustrates the practice of thedisclosed method.

EXAMPLE

6.25 g of n-butyl polytitanate (TYZOR® BTP, sold by E. I. Du Pont DeNemours And Company Corporation, Wilmington, Del.) was mixed and reactedwith 4.46 g of benzoylacetone (BzAc, Aldrich) to synthesize the chelatedoligomeric titanate (OT). The mixture was stirred for 2 hours at roomtemperature. 20 wt % propylene glycol propyl ether (PGPE) solutions ofthe chelated OT were spun-cast onto a water-soluble PVA templateobtained from Transfer Device Incorporated. A silicon wafer substratewas laminated on top of OT coated template by passing the substrate andOT coated template through a pair of rubber rolls. The chelatedoligomeric OT was UV-irradiated for 1 min with a dose of 100 mJ/cm2 at365 nm (OAI high pressure short arc lamp with 365 nm filter from OrielCo.) to set the oligomeric OT. The PVA template was then dissolved bydipping the sample into water. The samples were baked at 450° C. for 2hours to crystallize the structures into anatase titania andsimultaneously remove any organic components in the OT. FIG. 4 shows SEMmicrographs at two magnifications of the crystalline titaniananostructure after the calcining heat treatment. FIG. 5 shows AFMimages of the titania nanostructures after heat treatment. A grazingincident angle X-ray diffraction pattern of the titania film afterbaking at 450° C. for 2 hours is shown in FIG. 6, which indicates theanatase phase of titania. A high resolution transmission electronmicrograph (HRTEM) image in FIG. 7 shows the nanocrystalline structureof the titania film.

The singular forms “a,” “an,” and “the” include plural referents unlessthe context clearly dictates otherwise. The endpoints of all rangesdirected to the same characteristic or component are independentlycombinable and inclusive of the recited endpoint. All amounts, parts,ratios and percentages used herein are by weight unless otherwisespecified.

This written description uses an example to disclose the invention,including the best mode, and also to enable any person skilled in theart to practice the invention, including making and using any devices orsystems and performing any incorporated methods. The patentable scope ofthe invention is defined by the claims, and can include other examplesthat occur to those skilled in the art. Such other examples are intendedto be within the scope of the claims if they have structural elementsthat do not differ from the literal language of the claims, or if theyinclude equivalent structural elements with insubstantial differencesfrom the literal languages of the claims.

1. A method of forming a metal oxide nanostructure, comprising:disposing a chelated oligomeric metal oxide precursor on asolvent-soluble template to form a first structure comprising adeformable chelated oligomeric metal oxide precursor layer; setting thedeformable chelated oligomeric metal oxide precursor layer to form asecond structure comprising a set metal oxide precursor layer;dissolving the solvent-soluble template with a solvent to form a thirdstructure comprising the set metal oxide precursor layer; and thermallytreating the third structure to form the metal oxide nanostructure. 2.The method of claim 1, wherein the metal is selected from the groupconsisting of transition metals, zinc, aluminum, gallium, indium,thallium, germanium, tin, lead, antimony, bismuth, and combinationsthereof.
 3. The method of claim 1, wherein the chelated oligomeric metaloxide precursor comprises titanium.
 4. The method of claim 1, whereinthe solvent-soluble template is dissolved with an acidic, basic orneutral aqueous solution.
 5. The method of claim 1, wherein thesolvent-soluble template consists essentially of poly(vinyl alcohol). 6.The method of claim 1, wherein the setting involves heating the firststructure.
 7. The method of claim 1, wherein the setting involvesirradiating the first structure with UV light, electron beam, orionizing radiation.
 8. The method of claim 1, wherein the chelatedoligomeric metal oxide precursor comprises a chelated oligomerictitanate derived from the reaction of n-butyl polytitanate and achelating agent.
 9. The method of claim 8, wherein the chelating agentis selected from the group consisting of beta-diketone, beta-keto acid,beta-keto ester, beta-keto amide, malonic diester, malonic diamide, andcombinations thereof.
 10. The method of claim 1, wherein the metal oxidenanostructure is nonporous after thermal treatment.
 11. The method ofclaim 1, wherein the metal oxide nanostructure is porous after thermaltreatment.
 12. The method of claim 1, wherein thermally treatinginvolves heating the third structure at a temperature of about 450° C.to about 650° C. for a period of 30 minutes to 24 hours.
 13. A method offorming a metal oxide nanostructure, comprising: disposing a chelatedoligomeric metal oxide precursor on a solvent-soluble template to form afirst structure comprising a chelated oligomeric metal oxide precursorlayer having an exposed surface; bonding a substrate to the exposedsurface of the chelated oligomeric metal oxide precursor layer to form asecond structure comprising a chelated oligomeric metal oxide precursorlayer; setting the chelated oligomeric metal oxide precursor layer ofthe second structure to form a third structure comprising a set metaloxide precursor layer; dissolving the solvent-soluble template with asolvent to form a fourth structure comprising the set metal oxideprecursor layer; and thermally treating the fourth structure to form afifth structure comprising a metal oxide nanostructure bonded to thesubstrate.
 14. The method of claim 13, wherein the substrate is selectedfrom the group consisting of silicon, germanium, silicon-germaniumalloy, silicon carbide and silicon-germanium carbide alloy, galliumarsenide, indium arsenide, and indium phosphide.
 15. The method of claim13, wherein the substrate comprises a conductive metal or a conductivemetal oxide deposited on quartz or glass, the conductive metal selectedfrom the group consisting of titanium, manganese, iron, nickel, copper,zinc, molybdenum, palladium, silver, platinum, gold; magnesium,aluminum, gallium, indium, tin, and combinations of the foregoingmetals.
 16. The method of claim 13, wherein the substrate comprises aconductive metal oxide deposited on quartz or glass, wherein theconductive metal oxide is selected from the group consisting of tinoxide, fluorinated tin oxide, indium tin oxide, zinc oxide, andcombinations thereof.
 17. The method of claim 13, wherein bondingcomprises pressure lamination.